WO2000052523A1 - Electrochromic element - Google Patents

Abstract

The invention relates to an electrochromic element with an electrochromic arrangement that is enclosed between two planar substrates. Said arrangement comprises at least two electrode layers, an electrochromic layer, an ion storage layer and a polymer electrolyte layer which is formed in situ and which is adjacent to a sealing element towards the edge of the electrochromic element. According to the invention, the sealing element consists of a liquid proof, plastically deformable adhesive stripe (8) that is directly adjacent to the polymer electrolyte layer (7) and is arranged between the two substrates (1, 2). The adhesive stripe consists of a polyacrylate. A sealing line (9) made of a gastight sealant that is chemically compatible with the adhesive stripe is joined to the exterior of said adhesive stripe.

Description

 Electrochromic element

description

The invention relates to an electrochromic element with an electrochromic arrangement enclosed between two flat substrates, which comprises at least two electrode layers, an electrochromic layer, an ion storage layer and an in-situ polymer electrolyte layer, the polymer electrolyte layer towards the edge of the electrochromic element at least partially adjacent sealing element arranged between the two flat substrates.

Electrochromic elements of the aforementioned structure are known from a large number of publications. Among other things, you will used for displays, dimmable mirrors and ner glazing with variable light transmission. The flat substrates, which can be flat or curved, usually consist of inorganic glass panes for large-area glazing. However, you can also use other materials, e.g. Plastics. For the long-term stability of the electrochromic element, it is essential that the substrates are sufficiently impermeable to substances present in the environment, in particular to gases present in the ambient air. You must also reliably the electrochromic arrangement against the migration of volatile components such as Protect plasticizers, solvents, etc. These requirements are met particularly well by inorganic glass panes. For the sake of simplicity, glass panes will therefore usually be referred to below in connection with the flat substrates, although the invention is not restricted to this.

At least one of the electrode layers must be translucent. Usually one works for both electrode layers with transparent conductive metal oxide layers (TCO's), for example made of ITO or doped tin oxide. The electrode layers serve to be able to apply an electrical voltage to the electrochromic arrangement, with which the light transmission can be changed. For the electrochromic layer mostly materials based on tungsten oxide are used, whose light transmission can be changed by the incorporation of cations such as H ⁺ , Li ⁺ , Νa ⁺ etc. As a counterpart, the electrochromic layer requires an ion storage layer, also known as a counter electrode, for which a large number of materials are known, including, in particular, certitan oxide and Va nadium titanium oxide.

The electrochromic layer and the ion storage layer are separated by an ion conducting layer (electrolyte) ensuring the ion transport between the two. The use of polymer electrolyte layers formed in situ has proven particularly useful for large-area electrochromic elements. The polymer electrolyte layers are formed by a Monomers and at least one conductive salt-containing liquid mixture are introduced (injected) between the glass panes and polymerized there. The polymer electrolyte layers can be present in solid, gel or liquid form in the finished electrochromic element. They border on the edge of the electrochromic element to a sealing element.

The primary function of the edge-side sealing element is to seal the electrochromic arrangement arranged between the glass panes permanently liquid-tight and gas-tight towards the edge of the electrochromic element. In particular, it must be prevented that oxygen or water vapor present in the ambient air penetrate into the system. As part of the manufacture of the electrochromic element, the sealing element also takes on the task of enclosing the monomer mixture which is introduced between the glass panes in a liquid-tight manner. Such monomer mixtures often have a very low viscosity, which can be lower than that of water, so that even small leaks or pores in the sealing element would lead to the undesired outflow of the monomer mixture. Finally, the sealing element also serves as a spacer between the glass panes before the polymer electrolyte layer has solidified to such an extent that it takes on this function itself.

From EP 0 836 932 AI an electrochromic element with the features of the preamble is known, in which a sealing element directly adjoins the polymer electrolyte layer, which consists of a material that does not chemically react with the components of the electrochromic arrangement, in particular with the polymer electrolyte layer liquid and gas-tight sealant. Butyl sealants based on polyisobutylene, which have a particularly high gas diffusion tightness, are mentioned as being suitable for this purpose. The sealing element is not arranged between the glass panes, but closes a step formed on the edge side by the glass panes and the electrochromic arrangement. Given- if a liquid-tight seal can be provided. Attempts by the applicant have shown that sealing elements made of butyl sealants, which assume the main sealing function here, become detached from the polymer electrolyte layer at least in certain areas in the course of the polymerization, which can lead to premature aging in these areas. In addition, it is extremely difficult to find a suitable sealant that is so well compatible with materials commonly used for the polymer electrolyte layer that there is no material exchange or even an (electro) chemical reaction between the two materials over a long period of time.

It is the object of the invention to make electrochromic elements of the abovementioned construction permanently gas-tight, interfering interactions of the sealing element with the polymer electrolyte layer formed in situ or with other constituents of the electrochromic arrangement being avoided. Tearing off the sealing element from the polymer electrolyte layer during its polymerization should be avoided. The sealing element is also intended to enable the production of the electrochromic element, in particular the introduction of the monomer mixture required for the formation of the polymer electrolyte layer, using customary production methods and to reliably keep the flat substrates at a distance, at least during the production process.

This object is achieved by an electrochromic element with the features of claim 1. Advantageous refinements are the subject of the dependent claims.

According to the invention, it is provided that the sealing element consists of a plastically deformable, liquid-tight adhesive strip made of a polyacrylate, which adjoins the polymer electrolyte layer and the mutually facing surfaces of the two flat substrates (glass panes), and an adjoining it to the outside, at least partially between the two flat substrates arranged sealing strand consists of a gas-tight sealant that is chemically compatible with the adhesive strip.

Surprisingly, by using a sealing element according to the invention consisting of at least two separate functional components, all of the functions required for the production and permanent operation of an electrochromic element can be achieved. to provide. The adhesive strip primarily takes on the function of an edge seal for the polymer electrolyte layer that prevents the liquid monomer mixture from flowing away and also acts as a spacer for the glass panes. Due to its plasticity, the adhesive strip can follow the polymer electrolyte layer shrinking in the course of the polymerization and does not tear off from it, like other known sealing elements. Polyacrylate materials are chemically well compatible with a number of materials that can be used for the polymer electrolyte layers, but in particular with polymer electrolyte layers based on (meth) acrylic acid esters, which have proven particularly useful for this purpose.

The polyacrylate adhesive strip according to the invention is liquid-tight, but not gas-tight. In particular, it is not sufficiently diffusion-tight against gases such as oxygen and water vapor and against solvents such as propylene carbonate or ethylene carbonate. The adhesive strip is therefore functionally supplemented within the scope of the invention by a sealing strand made of a highly gas-tight sealant that is chemically compatible with the adhesive strip.

It has been shown that polyacrylate adhesive strips are particularly suitable as a type of buffer or adapter between the materials of the polymer electrolyte layer on the one hand and the sealants of the sealing strand on the other. The presence of such a buffer compatible with both materials allows the use of a greater variety of sealants than if they were to be directly adjacent to the polymer electrolyte layer and had to be (electro) chemically compatible with it.

The adhesive strip preferably consists of an adhesive tape, available as a roll, made of a polyacrylate, which has a glass transition temperature of less than 20 ° C. The glass transition temperature is preferably well below 20 ° C., in particular below 10 ° C.

Such adhesive tapes are manufactured and sold, for example, by 3M under the trade names Scotch Acrylic Foam or Scotch Isotac. Such tapes can be processed well at room temperature. They adapt easily to the contour of the adjoining surfaces and show a kind of self-healing effect, so that there are puncture openings between the injection of the monomer mixture and the injection tools Glass panes are formed and quickly close again after removing the tools. In addition, when selecting the material for the adhesive tape, it is advisable to ensure that the material has a low to medium degree of crosslinking. This ensures that the stickiness of the material is sufficiently high. Before the components of the electrochromic element are assembled, the adhesive tape is applied either manually or by machine to the edge of one of the glass panes. A transparent adhesive tape is preferably used. Since the edge area of the electrochromic element is usually covered by frames, colored or opaque adhesive tapes can also be used.

For permanent functioning of electrochromic elements, such adhesive strips made of polyacrylate are particularly suitable, the water content of which is at most 0.3 percent by weight. The water content is preferably below 0.05 percent by weight. If necessary, the adhesive strip must be subjected to a suitable drying treatment before use. If the adhesive strip has a higher water content, there is a risk of this water diffusing into the polymer electrolyte layer, which can lead to blistering and premature aging.

The adhesive strip preferably has a width of at least 5 mm and a maximum of 20 mm. With smaller widths the handling and the achievement of the liquid tightness are made more difficult, while with larger widths the ratio of usable area to the total area of the electrochromic element deteriorates without its properties still improving significantly.

A highly gas-tight butyl sealant based on polyisobutylene or butyl rubber or an epoxy sealant is preferably used for the sealing strand. Preferred materials are those which, in order to avoid leakage currents in the case of butyl sealants, have a specific electrical conductivity of less than 10 ^"9 Ω ^{" 1-} cm ^{~ 1} , preferably less than 10 ^"11 Ω ^' ^ cm ^{" 1} , and in the case of epoxy sealants have a specific electrical conductivity of less than 10 ^"12 Ω ^{" 1-} cm ^"1 , preferably less than 10 ^{" 13} Ω ^{" •} cm ^{" 1} . In both cases, the water vapor permeability according to DLN 53122-1.2 (according to prEN 1279-4) should be at most about 4.0 gm ^"2 -d ^"] . The water vapor permeability is determined according to the standard on 2 mm thick films from the determined material.

The above-mentioned sealant materials are chemically particularly well compatible with the polyacrylate materials used according to the invention for the adhesive strip and have excellent diffusion tightness against gases such as oxygen and water vapor as well as solvents such as e.g. Propylene carbonate or ethylene carbonate. Other materials known and customary as sealants can also be used, provided they ensure a comparable tightness to the gases mentioned as the materials preferred in the context of the invention and are compatible with the polyacrylate adhesive strip. The person skilled in the art can determine this by simple experiments.

Preferred butyl sealants are e.g. Bostik 5124 or 5125 (company Bostik) based on a butyl rubber with the following properties:

9 1

Water vapor permeability: about 0.10 - 0.15 gm ^" -d ^" specific electrical conductivity: about 10 ^"11 Ω ^ -cm ^{" 1}

Preferred epoxy sealants are e.g. Araldit 2012 or 2014 (Ciba-Geigy) with the following properties:

9 1

Water vapor permeability: about 4.0 gm ^" -d ^" specific electrical conductivity: about 10 ^"14 Ω ^ -cm ^{" 1}

or Eccobond 45 (Grace Specialty Polymers / Emerson & Cuming) with the following properties:

9 1

Water vapor permeability: about 2.5 gm ^" -d ^" specific electrical conductivity: about 3 - 10 ^" 14

It goes without saying that a sealant, in particular based on butyl rubber, polyisobutylene or epoxy resin, must be electrochemically inert in the function of sealing an electrochromic unit in the electrical voltage range required for the function of the electrochromic element. This means that the sealant must not show any electrochemical decomposition reactions when an electrical potential of, for example, 3 or 5 volts is applied. It also goes without saying that the sealing strand, like the adhesive strip, must be arranged over the entire circumference of the pane between the glass panes in order to enclose the electrochromic element with the glass panes in a diffusion-tight manner. The sealing strand does not have to be flush with the edge of the pane. Rather, it can at least partially cover the edges of the pane.

It can be advantageous if the electrochromic element is sealed to the outside in a manner known per se with a further strand of sealant. Polysulfide-based materials are particularly suitable for this purpose in the production of insulating glass. This is particularly useful if the electrochromic element is assembled with at least one further glass pane to form an insulating glass unit.

The sealing strand preferably borders directly on the adhesive strip. However, it is within the scope of the invention to have at least one further functional component, e.g. a separating layer or an adhesion promoter layer to be provided if the benefits achieved thereby are justified by the additional effort required for this. Provision can also be made to provide the glass panes with an adhesion promoter in the region of the adhesive strip, the sealing strand or an additional sealant strand in order to improve the adhesion of these materials to the glass.

The invention can be used with particular advantage in the case of electrochromic elements having a polymer electrolyte layer which, in addition to the proportion of conductive salt required for the provision of a sufficient amount of cations (for example in accordance with WO 95-31746 A1), has at least one (meth) acrylic acid ester, at least one plasticizer and has at least one polymerization initiator (EP 0 683 215 AI).

The invention is explained in more detail below with reference to the embodiments shown in the figures. It shows:

1 shows a first embodiment of an electrochromic element according to the invention in cross section, FIG. 2 shows a second embodiment of an electrochromic element according to the invention corresponding representation.

The illustration in the figures is to be understood as a basic illustration. The dimensions are not to scale.

The electrochromic element according to FIG. 1 consists of two 4 mm thick transparent float glass panes 1 and 2, each of which has transparent electrode layers 3, 4 made of indium tin oxide (ITO), fluorine-doped tin oxide or another electrically conductive metal oxide on their mutually facing surfaces are provided. An electrochromic layer 5 made of tungsten oxide is arranged on the electrode layer 3, while an ion storage layer 6 made of one or more metal oxides, such as e.g. Cerium, vanadium, titanium, zirconium or nickel oxide. The edge area of the electrode layers 3, 4 is in each case uncoated over a range of a few millimeters, as can be seen in the figure. The busbars via which an electrical voltage is applied to the electrode layers 3, 4 are not shown.

Between the coated glass panes 1 '2 there is a 0.9 mm thick, in situ polymerized polymer electrolyte layer 7 according to EP 0 683 215 Al with a proportion of conductive salt according to WO 95-31746 Al. It borders directly on a 0.9 mm thick and 9 mm wide transparent adhesive strip 8 made of a low-crosslinked polyacrylate, which is formed from an adhesive tape from 3M with the corresponding dimensions and sold under the trade name Scotch Isotac VHB 4910 and subjected to a drying treatment before application has been. The polyacrylate of this adhesive tape has a glass transition temperature between 5 and 10 ° C. The glass transition temperature was determined by dynamic thermomechanometry (see e.g. "Investigation methods in chemistry", Georg Thieme Verlag, 2nd edition 1990, chapter 1, p. 13).

The circumferential groove remaining between the outer surface of the adhesive strip 8 facing the edge of the electrochromic element and the outer edges of the glass panes 1, 2 is filled with a sealing strand 9 made of an Araldit 2012 epoxy sealant. The sealing strand 9 is essentially flush with the outer edges of the glass panes 1, 2. However, it could also cover these edges at least in certain areas. FIG. 2 shows in cross section an edge section of an insulating glass unit formed with an electrochromic element according to the invention. The embodiment of the electrochromic element according to FIG. 2 differs from that in FIG. 1 in that the glass pane 1 has smaller outer dimensions than the glass pane 2. As in the previous example, an adhesive strip 8 made from Scotch Isotac VHB 4910 adhesive tape from 3M is provided, which directly adjoins the polymer electrolyte layer 7. In this case, the width of the adhesive strip 8 is chosen to be somewhat smaller, at 6 mm, than in the previous example, in order to at least partially compensate for the loss of available visible area, which is caused by the stepped design of the electrochromic element. A sealing strand 9 formed in this case from a butyl sealant Bostik 5125 borders on the adhesive strip 8. The step formed by the two glass panes 1, 2 and by the outer surface of the sealing strand 9 is made with a further sealant strand 10 made of a polysulfide insulating glass adhesive, for example from Polysulfide Naftotherm M 82 from Chemetall, filled out. The sealant strand 10 is only shown in sections, while all other components of the insulating glass unit, such as the spacer and the at least one further glass pane, have been completely omitted. The structure of insulating glass panes is generally known, so that there is no need to describe further details in this connection.

The two electrochromic elements shown in the figures passed various aging tests without visible damage.

Claims

Expectations 1. Electrochromic element with an electrochromic arrangement enclosed between two flat substrates, which comprises at least two electrode layers, an electrochromic layer, an ion storage layer and an in-situ polymer electrolyte layer, the polymer electrolyte layer towards the edge of the electrochromic element towards at least partially Adjacent sealing element arranged between the two flat substrates, characterized in that the sealing element consists of a plastically deformable, liquid-tight adhesive strip (8), which is arranged between the two flat substrates (1, 2) and directly adjoins the polymer electrolyte layer (7) Polyacrylate and a sealing strand (9) adjoining it outwards and at least partially arranged between the two flat substrates (1, 2) consists of a gas-tight sealant that is chemically compatible with the adhesive strip (8). 2. Electrochromic element according to claim 1, characterized in that the adhesive strip (8) is formed from a polyacrylate adhesive tape. 3. Electrochromic element according to claim 1 or 2, characterized in that the adhesive strip (8) has a width of at least 5 mm. 4. Electrochromic element according to claim 3, characterized in that the adhesive strip (8) has a maximum width of 20 mm. 5. Electrochromic element according to one of the preceding claims, characterized in that the adhesive strip (8) consists of a polyacrylate with a water content of at most 0.3 percent by weight, preferably less than 0.05 percent by weight. 6. Electrochromic element according to one of the preceding claims, characterized in that the adhesive strip (8) consists of a polyacrylate with a glass transition temperature below 20 ° C, preferably below 10 ° C. 7. Electrochromic element according to one of the preceding claims, characterized in records that the sealing strand (9) consists of a butyl sealant based on polyisobutylene or butyl rubber. 8. Electrochromic element according to claim 7, characterized in that the sealing strand (9) has a specific conductivity of less than 10 ^"9 Ω ^ -cm ^{" 1} , preferably less than 10 ^"11 Ω ^ -cm ^{" 1} , and a water vapor permeability according DIN 53122-1.2 of less than 0.5 gm ^"2 -d ^{" 1} . 9. Electrochromic element according to one of claims 1 to 6, characterized in that the sealing strand (9) consists of an epoxy sealant. 10. Electrochromic element according to claim 9, characterized in that the sealing 19 1 1 cable strand (9) a specific conductivity of less than 10 ^" Ω ^" -cm ^" , preferably less than 10 ^{" 13} Ω ^"1 -cm ^{" 1} , and a water vapor permeability according to DIN 53122-1.2 of less than 4.0 gm ^ -d ^"1 . 11. Electrochromic element according to one of the preceding claims, characterized in that at least one further sealant strand (10), in particular based on polysulfide, is adjacent to the sealing strand (9). 12. Electrochromic element according to one of the preceding claims, characterized in that the polymer electrolyte layer (7) comprises at least one (meth) acrylic acid ester, at least one plasticizer and at least one polymerization initiator.